Use as a base image

One may base one's own images on this karm/mod_cluster-master-dockerhub as simply as with creating a Dockerfile:

FROM karm/mod_cluster-master-dockerhub:latest
MAINTAINER Your identity of choice <your email>
# Your own configuration located in the same directory as your Dockerfile
COPY mod_cluster.conf ${HTTPD_MC_BUILD_DIR}/conf/extra/mod_cluster.conf
# Your own entry point script located in the same directory as your Dockerfile
COPY docker-entrypoint.sh /

Note that HTTPD_MC_BUILD_DIR as well as other ENV constants are propagated to your Dockerfile.